The use of compositions based on conventional ethylene homopolymer or copolymers in the manufacture of stretch wrap films having good cling and optical properties is known, e.g., as shown in U.S. Pat. No. 4,073,782. This patent discloses stretch wrap films made from a ternary composition wherein the resin component is a polyethylene, a copolymer of ethylene and vinyl acetate, or a mixture of the above-mentioned polyethylene and copolymer. The remaining essential components of the ternary composition are sorbitan monooleate, which is mainly added as an antihazing agent, and a liquid paraffin, as an adhesiveness modifier. Although the films produced in accordance with the teachings of the aforementioned patent perform very well in some applications, their strength and toughness properties are generally not as good as would be desired.
The recently developed linear low density polyethylenes have the desired strength and toughness properties required from stretch wrap applications, but do not possess the required cling, which in the case of conventional polyethylene, can be partially obtained by incorporation of vinyl acetate as a comonomer.
U.S. Pat. No. 4,436,788 discloses a composite stretch wrap film constituted of a layer of ethylene-vinyl acetate copolymer containing a tackifier and a layer of linear low density polyethylene. Such a film exhibits a certain amount of adherence to itself, however, in certain applications requiring very thin films, acceptable adherence can be achieved only after applying heat to the overlapping wraps of the film.
The patent also discloses a three-layer stretch wrap film of improved cling properties constituted of an inner layer of linear low density polyethylene and the two outer layers of ethylene-vinyl acetate copolymer preferably containing a tackifier. It has been found that the presence of tackifier is necessary in both of the outer layers in order to provide sufficient cling. However, because of the presence of such a tackifier in the outer layers, it has not been possible to use this film in the manufacture of printed films of acceptable print quality. The tackifiers work by migrating to the surface of the film. Due to the presence of these tackifiers on the surface, it is impossible to hold a corona treatment level on the film which is necessary to wet out printing inks. Also, because the inner linear low density polyethylene layer by necessity must be very thin when the composite film is required to be of thin gauge, the strength of the stretch wrap is less than desired.
It is therefore an object of the present invention to provide a novel composite stretch wrap film which exhibits sufficient cling and strength without the necessity of heat treatment.
It is another object of the invention to provide a printable composite stretch wrap film exhibiting excellent cling properties even at thin film gauges.
Further objects of the invention will become apparent from a reading of the specification and appended claims.